Horseshoe kidney is one of the most common renal fusion anomalies, found in approximately 1 in 400-500 adults. It exists when the lower poles of the kidney are fused together during development as a fetus. 

Most of the time, a horseshoe kidney is an incidental find on an exam for some other condition that the patient is having. In this case the patient had a pelvic pain and US revealed a large ovarian cyst and the gynecologist requested CT for abdomen and pelvis.

CT is probably the study of choice as it can show the complications that may associate the anomaly e.g. renal calculi and obstructive uropathy.